The data systems on board an aircraft, such as an aeroplane, comprise aerodynamic and thermodynamic sensors and their associated electronics which measure the characteristics of the air stream surrounding the aeroplane and convert this information into electrical signals. These sensors comprise transducers, rotating electrical machines, or, more generally, resolvers, or pressure difference devices, the signals of which are processed to obtain flight parameters such as the angle of attack and the side slip angle.
These sensors are situated at specific points of the cockpit of the aeroplane. They are in particular temperature sensors, rotating fins or multifunction devices incorporating probes of tube type (“tube-slot”) with self-alignment capabilities.
Such instrumentation exhibits drawbacks such as a sensitivity to electromagnetic threats, heavy weight, a relatively large volume, a need for several power supply voltages, etc. Furthermore, the high accuracy of certain sensors can lead to high costs, and condition the technology to be employed and the positioning of these sensors.
In the aeroplanes, the data originating from the onboard sensors make it possible to provide information to the pilot. Some of these data relate to particular measurements, which are those of the angle of attack and the side slip angle. Currently, these measurements are performed using specific rotating electrical machines.
The angle of attack is an angle measured in the normally vertical plane X-Z of symmetry of an aeroplane. More specifically, this angle is measured relative to a reference line, which is a line linking the leading edge and the trailing edge at median points on a wing. Most commercial aeroplanes use the central line or the longitudinal axis of the fuselage as reference line. The angle of attack is defined as the angle at which the relative wind encounters the reference line of the wing or of the fuselage.
The side slip angle is the angle between a vector, called aeroplane speed vector, and the longitudinal axis thereof.
To measure the angle of attack and the side slip angle of an aeroplane, there are in particular known:                a measurement method based on probes using fins that can move in rotation,        a measurement method based on probes using pitot tubes and/or holed surfaces and/or tubes.        
A probe 16 using a fin that can move in rotation is represented in FIGS. 1A to 1C and 2. With such a probe, it is possible to measure the angle of attack as follows. A fin 10 is oriented in the direction of the local air stream, parallel to the relative wind of the apparatus. Electronic means make it possible to determine the angle between the local air stream and a reference axis of the aeroplane, in order to then estimate, by difference, the angle of attack. The fin is mounted to move in rotation on a central axis 14 of a cylindrical housing 11. The latter is closed at both of its ends, and is also provided, on the one hand, with a connector 13 and, on the other hand, with a plate 12 pierced with a central circular orifice which is passed through by the axis 14.
A measurement method based on the use of this type of device is commonly used to measure the angle of attack and the side slip angle. The measurement of these angles makes it possible to know if the aeroplane is within the flight envelope limits specified by the aeroplane manufacturer.
The fin 10 illustrated in FIGS. 1A to 1C can revolve freely by a given angle, so as to be positioned in a local air flow in line with the probe and parallel thereto.
The rotation of the fin is transmitted to the axis 14, on which it is mounted, and which is in turn coupled to a rotary position transducer 15 with brushless resolver. The electrical signal generated by the latter can then be processed by a processing circuit and be converted into a digital signal, which can be transmitted to the onboard computer via a data bus.
Such a probe with rotating fin from the known art can also use an actively controlled slot heating technology, in order to de-ice the fin in all icing conditions.
The document FR 2922301 (or US 2009 099811) describes the use of such a probe which, as illustrated in FIG. 3, is positioned on the surface of the fuselage of an aeroplane 17, in the front part thereof, precisely in the region situated in front of the cockpit 18 (the term “front” being understood in the conventional manner, that is to say towards the nose 19 of the aeroplane, in the direction X). The measured side slip angle β is thus the angle formed locally between the orientation of the speed vector of the flow of the air in line with the probe {right arrow over (V)} and the direction X projected in a horizontal plane. Other side slip probes can be provided on the surface of the fuselage of the aeroplane, such as, for example, probes 16′, 16″.
Such a probe with rotating fin from the known art presents the following drawbacks:                its volume is large and can lead to integration difficulties because of the reduced space available,        its weight is heavy: approximately 1925 kg per probe.        